A type of a cooler for cooling semiconductor modules or electronic components is known. This cooler is configured to jet coolant toward an inner surface of a cooling plate where a heating element, such as a semiconductor module, is attached. This type of cooler is called an impinging jet cooler. An impinging jet type double-sided cooler in which a heating element is attached to an outer surface of each of two cooling plates facing each other, and that jets the coolant onto inner surfaces of the respective cooling plates has been proposed (for example, Japanese Patent Application Publication Nos. 2015-133420 and 2015-149361). Double-sided coolers in Japanese Patent Application Publication Nos. 2015-133420 and 2015-149361 are provided with the following structure. A coolant flow path between a pair of cooling plates facing each other is segmented into three layers in a normal direction of the cooling plates by two inner plates. Coolant is supplied to a space in the middle. The inner plates are provided with nozzles for jetting the coolant toward the outer cooling plates. The coolant, which is supplied to the space in the middle, is jetted, through the nozzles of the inner plates, toward the cooling plates facing the respective inner plates.